The present invention relates generally to lithography, and particularly to optical photolithography glass for use in optical photolithography systems utilizing vacuum ultraviolet light (VUV) wavelengths below 193 nm, preferably below 175 nm, preferably below 164 nm, such as VUV projection lithography systems utilizing wavelengths in the 157 nm region.
The invention relates to VUV transmitting glass that is transmissive at wavelengths below 193 nm, in particular, a photomask silicon oxyfluoride glass suitable for use in the Vacuum Ultraviolet (VUV) 157 nm wavelength region.
Refractive optics requires materials having high transmittance. For semi-conductor applications where smaller and smaller features are desired at the 248 and 193 nm wavelengths, high purity fused silica has been show to exhibit the required minimum transmittance of 99%/cm or better.
Projection optical photolithography systems that utilize the vacuum ultraviolet wavelengths of light below 193 nm provide benefits in terms of achieving smaller feature dimensions. Such systems that utilize vacuum ultraviolet wavelengths in the 157 nm wavelength region have the potential of improving integrated circuits with smaller feature sizes. Current optical lithography systems used by the semiconductor industry in the manufacture of integrated circuits have progressed towards shorter wavelengths of light, such as the popular 248 nm and 193 nm wavelengths, but the commercial use and adoption of vacuum ultraviolet wavelengths below 193 nm, such as 157 nm has been hindered by the transmission nature of such vacuum ultraviolet wavelengths in the 157 nm region through optical materials. Such slow progression by the semiconductor industry of the use of VUV light below 175 nm such as 157 nm light has been also due to the lack of economically manufacturable photomask blanks from optically transmissive materials. For the benefit of vacuum ultraviolet photolithography in the 157 nm region such as the emission spectrum VUV window of a F2 excimer laser to be utilized in the manufacturing of integrated circuits there is a need for mask blanks that have beneficial optical properties including good transmission below 164 nm and at 157 nm and that can be manufactured economically.
The present invention overcomes problems in the prior art and provides a economical high quality improved photomask blanks and VUV transmitting lithography glass that can be used to improve the manufacturing of integrated circuits with vacuum ultraviolet wavelengths.
Use of high purity fused silica as optical elements in photolithography stems from the fact that high purity fused silica is transparent over a wide range of wavelengths, spanning from the infrared to deep ultraviolet regions. Furthermore, high purity fused silica exhibits excellent chemical durability and dimensional stability.
It has been suggested in EP 0 636 586 A1 that in order to be suitable for use as a photomask substrate for certain photolithography applications at 248 and 193 nm wavelengths, high purity fused silica made by the direct flame method must contain high molecular hydrogen in the range of 1017 to 1019 molecules/cm3. Similarly, JP 1-201664 discloses that synthetic quartz glass for use as photomask material whose optical properties have been changed due to sputtering, plasma etching or excimer irradiation, can be restored to its original condition by heat treating the glass in a hydrogen atmosphere. Specifically, this document describes the effect on synthetic quartz of exposure to 248 and 193 run wavelengths. The effect of exposure to 248 and 193 nm wavelengths on fused silica is also described in xe2x80x9cDensification of Fused Silica under 193 nm excitation,xe2x80x9d by Borrelli et al, in J. Opt. Soc. Am. B/Vol. 14, No. 7, pp. 1606-1615 (July 1997); and by Allan et al., in xe2x80x9c193-nm excimer-laser-induced densification of fused silica,xe2x80x9d Optics Letters, Vol. 21, No. 24, pp. 1960-1962 (Dec. 5, 1996).
EP 0 901 989 A1 discloses a manufacturing method for making silica glass substantially free of chlorine. In a direct deposit concurrent vitrifying process silicon tetrafluoride is flame hydrolyzed to provide a silica glass in which fluorine is controlled within the range 100 ppm to 450 ppm and OH group density in the range from 600 ppm to 1300 ppm.
U.S. Pat. No. 5,326,729 discloses quartz glass having excimer laser resistance produced by subjecting the glass to dehydration treatment in a temperature range lower than the transparent vitrification temperature of the glass followed by transparent vitrification and molding to a desired shape, followed by a doping treatment in a hydrogen atmosphere.
U.S. Pat. No. 5,474,589 discloses a UV light permeable fluorine-doped synthetic quartz glass with decreased defects.
Applicants, previously have disclosed several effective methods for improving the optical properties of high purity fused silica when used as an optical lens in photolithography at both the 248 and 193 nm wavelength regions. See for example, U.S. Pat. Nos. 5,616,159; 5,668,067 and 5,735,921 all incorporated herein by reference.
Accordingly, it is an object of the present invention to disclose VUV transmitting dry direct deposit vitrified silicon oxyfluoride glasses for use at VUV wavelengths below 193 nm, preferably in the F2 Excimer Laser 157 nm region, methods of making such glass, and methods of making dry direct deposit vitrified lithography glass articles.
In the present invention we disclose VUV transmitting dry direct deposit vitrified silicon oxyfluoride lithography glass suitable for use as optical elements, for use as a lens or preferably for use as a photomask substrate at VUV wavelengths below 193 nm. In particular, the inventive direct deposit vitrified silicon oxyfluoride glass production exhibits benifits tailored for optical lithography articles and applications in the photolithography VUV wavelength region around the 157 nm Excimer laser wavelengths and below 193 nm.
The object of the invention is achieved by use of a dry low hydroxy radical fluorine-doped SiO2 fused direct deposit vitrified synthetic silicon oxyfluoride glass which exhibits high transmittance in the vacuum ultraviolet (VUV) wavelength region while exhibiting excellent thermal and physical properties. By xe2x80x9cdryxe2x80x9d we mean having an OH content below 50 ppm by weight, preferably dehydrated-below 10 ppm OH by weight, and most preferably below 1 ppm by weight.
In another aspect, the object of the invention is further achieved by ensuring that the dry direct deposit vitrified silicon oxyfluoride glass is essentially free of chlorine.
In yet another aspect, the object of the invention is achieved by ensuring a low molecular hydrogen content in the dry direct deposit vitrified glass. By this we mean that the molecular hydrogen (H2)content is below 1xc3x971017 molecules/cm3.
In a preferred embodiment of the invention, the VUV transmitting dry direct deposit vitrified silicon oxyfluoride glass has a fluorine content in the range of 0.1 to 0.4 weight percent which inhibits laser exposure induced absorption and provides laser exposure durability with minimal transmission loss at 157.6 nm after prolonged exposure. The invention includes a below 193 nm VUV transmitting glass photomask substrate for photolithography at wavelengths of about 157 nm with the glass being a high purity dry direct deposit vitrified silicon oxyfluoride glass with an OH content below 50 ppm by weight, hydrogen content below 1xc3x971017 molecules/cm3 and a fluorine content in the 0.1 to 0.4 weight percent range.
The invention includes a process of making VUV transmitting glass silicon oxyfluoride glass that includes providing a hydrogen-free fuel carbon monoxide combustion burner; providing a heat containing direct deposit furnace; providing a supply of carbon monoxide and a supply of oxygen to said carbon monoxide combustion burner to form a carbon monoxide combustion reaction flame, providing a direct glass deposition surface proximate said flame, supplying a Si-glass precursor feedstock and a F-glass precursor feedstock to said carbon monoxide combustion burner wherein said Si-glass precursor feedstock and said F-glass precursor feedstock is reacted in said flame into a silicon oxyfluoride glass soot directed at said glass deposition surface, and said soot is concurrently directly deposited and vitrified into a dry direct deposit vitrified silicon oxyfluoride glass body.
The invention includes a dry direct deposit vitrified silicon oxyfluoride glass having essentially no OH groups, less than 5xc3x971016 molecules/cm3 of molecular hydrogen, and a fluorine content in the range of 0.1 to 0.4 weight %. The invention includes a dry direct deposit vitrified silicon oxyfluoride lithography glass having an OH content less than 5 ppm by weight, a Cl content less than 5 ppm by weight, a H2 content less than 1xc3x971017 molecules/cm3, and a fluorine content of 0.1 to 0.4 weight % with a 157 nm internal transmission of at least 85%/cm. The invention includes a VUV pattern printing method with the steps of providing a below 164 nm radiation source for producing VUV photons, providing a dry direct deposit vitrified silicon oxyfluoride glass having less than 5 ppm by weight OH, less than 5 ppm by weight Cl, a  less than 0.5 weight percent fluorine content, and 157 nm and 165 nm measured transmission of at least 75%/5 mm. The pattern printing method includes transmitting the VUV photons through the dry direct deposit vitrified silicon oxyfluoride glass, forming a pattern with the VUV photons and projecting the pattern onto a VUV radiation sensitive printing pattern. The invention includes a dry direct deposit vitrified VUV transmitting silicon oxyfluoride glass having a OH content less than 5 ppm by weight, a fluorine content of at least 0.1 weight %, the glass consisting essentially of Si, O, and F with an internal transmission in the wavelength range of 157 nm to 175 nm of at least 85%/cm and a 165 nm absorption less than 0.4 (absorption units/5 mm) after exposure to a 157 nm laser for 41.5 million pulses at 2 mJ/cm2-pulse.
The invention includes a below 193 nm VUV transmitting glass photomask substrate for photolithography at wavelengths of about 157 nm, said glass photomask substrate comprising a dry high purity direct deposit vitrified silicon oxyfluoride glass with an OH content below 20 ppm by weight, a Cl content below 0.1% by weight, and a fluorine content in the range of 0.01 to 7 weight percent.
The invention includes a method of making a below 193 nm VUV transmitting optical lithography glass for transmitting wavelengths of about 157 nm, said method comprising providing a hydrogen-free fuel carbon monoxide combustion burner; providing a supply of carbon monoxide and a supply of oxygen to said carbon monoxide combustion burner to form a carbon monoxide combustion reaction flame, providing a direct glass deposition surface proximate said flame, supplying a Si-glass precursor feedstock and a said F-glass precursor feedstock to said carbon monoxide combustion burner wherein said Si-glass precursor feedstock and said F-glass precursor feedstock is reacted in said flame into a silicon oxyfluoride glass soot directed at said glass deposition surface, and said soot is concurrently directly deposited and vitrified into a silicon oxyfluoride glass body.
The invention includes a method of making a homogeneous glass optical lithography element, said method comprising providing a hydrogen-free fuel carbon monoxide combustion burner; providing a supply of carbon monoxide and a supply of oxygen to said carbon monoxide combustion burner to form a carbon monoxide combustion reaction flame, providing a direct glass deposition surface proximate said flame, supplying a Si-glass precursor feedstock and a dopant R-glass precursor feedstock to said carbon monoxide combustion burner wherein said Si-glass precursor feedstock and said dopant R-glass precursor feedstock is reacted in said flame into a dry R doped silica glass soot directed at said glass deposition surface, and said soot is concurrently directly deposited and vitrified into a dry homogeneous R doped silica glass body, and forming said directly deposited vitrified glass body into a homogeneous glass optical lithography element. In preferred embodiments of the method of making dry R doped silica glass, the glass dopant R is chosen from the glass dopant group consisting of F, Ti, Ge, B, P, and Al.
The invention includes a method of making a homogeneous glass optical lithography element, said method comprising providing a hydrogen-free fuel carbon monoxide combustion burner; providing a supply of carbon monoxide and a supply of oxygen to said carbon monoxide combustion burner to form a carbon monoxide combustion reaction flame, providing a direct glass deposition surface proximate said flame, supplying a Si-glass precursor feedstock to said carbon monoxide combustion burner wherein said Si-glass precursor feedstock is reacted in said flame into a dry high purity silica glass soot directed at said glass deposition surface, and said soot is concurrently directly deposited and vitrified into a dry homogeneous high purity silica glass body, and forming said directly deposited vitrified glass body into a homogeneous glass optical lithography element.
The method of making below 193 nm VUV transmitting silicon oxyfluoride glass includes providing a hydrogen-free fuel combustion burner, with the preferred hydrogen-free fuel combustion burner being a carbon monoxide combustion burner. The method includes providing a supply of hydrogen-free carbon monoxide fuel and a supply of oxygen to the combustion burner to form a carbon monoxide combustion reaction flame which is contained within a heat containing direct deposit furnace. A direct glass deposition surface is provided in said furnace proximate and preferably below said carbon monoxide burner and flame. Alternative hydrogen-free fuel combustion fuels include carbon suboxide and carbonyl sulfide. a supply of carbon monoxide and oxygen to the combustion burner maintains the carbon monoxide flame to which is supplied a Si-glass precursor feedstock and a F-glass precursor feedstock. Preferably the Si-glass precursor feedstock is hydrogen free, such as silicon tetrachloride and silicon tetraisocyanate [Si(NCO)4].
The process and apparatus in accordance with one embodiment of the invention manufactures substantially water-free silica glass. The process and apparatus to make such water-free fused silica glass does so by eliminating the possibility of water ever forming in the combustion atmosphere. This is achieved in a first embodiment thereof by to utilizing a substantially hydrogen-free fuel, such as carbon monoxide (CO), carbon suboxide (C3O2), carbonyl sulfide (COS), and the like. Use of such substantially H-free fuels minimizes water formation in the combustion reaction. According to a preferred embodiment, it is desired to use a substantially hydrogen-free raw material as a glass precursor for silica also. Most preferably, a combination of substantially hydrogen-free raw material and substantially hydrogen-free fuel is utilized. Typical examples of substantially H-free glass precursors include silicon carbide (SiC), silicon monoxide (SiO), silicon nitride ((Si3N4), silicon tetrabromide (SiBr4), silicon tetrachloride (SiCl4), silicon tetraiodide (SiI4) and silica (SiO2). Si(NCO)4 may also be utilized.
In accordance with the invention, when carbon monoxide, for example, is used as the fuel and combined with oxygen, the only by-product is carbon dioxide. This by-product is easily disposed of and, advantageously, no water is formed from the process reaction. This reaction is illustrated by the following equation.
CO+xc2xdO2xe2x86x92CO2
It was recognized that the available heat from carbon monoxide is about one-fourth the heat available from natural gas (methane). Therefore, four times the fuel would be required to produce the same amount of heat. However, only one-half mole of combustion supporting oxygen is required to combust one mole of CO. Thus, the total volume of oxygen required is the same for either fuel to produce the same amount of heat. The following equation shows the required carbon monoxide fuel needed to match the available heat of combusting one mole of methane (CH4) used in one prior art process.
4CO+2O2xe2x86x924CO2
The equation below shows the by-products and combustion supporting oxygen needed for combustion of one mole of methane in the prior art.
CH4+2O2xe2x86x922H2O+CO2
Thus, from the foregoing, it should be recognized that the production of substantially water-free silica glass-is obtainable.
A method for producing a vitrified glass article is provided by the invention. The inventive method comprising several steps. First, heat is generated from a combustion burner having a flame produced by igniting a substantially hydrogen-free fuel. According to the invention, the flame is the only source of heat. Next, a glass precursor is flowed into the flame to produce silica-containing soot. Finally, the silica-containing soot is deposited onto a substrate and substantially simultaneously converted (by the heat of the flame) to form the vitrified glass article by the heat of the flame. In a preferred embodiment, soot is deposited onto a silica-containing glass member, such as a fused silica puck. According to this method, the vitrified glass article contains very low amounts of water. The step of depositing preferably takes place within a furnace chamber that may include a purge gas, such as nitrogen provided thereto. This method is adapted for producing homogeneous glass. According to the invention, a hydrogen-free fuel carbon monoxide combustion burner is utilized. The burner comprises a fume passage adapted to supply, at a first flow rate, a glass precursor, and a fuel passage surrounding the fume passage, the fuel passage adapted to supply a substantially hydrogen-free fuel at a flow rate at least 20 times the first flow rate. The burner may also include an inner shield passage between the fuel passage and the fume passage adapted to supply at least oxygen. The burner may further comprise an outer shield passage surrounding the fuel passage for introduction of additional gasses.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principals and operation of the invention.